12volt vs 6 volt Coil in 6 volt System

dorvedahl47pu

dorvedahl47pu

Senior Member
I've got two 1947-late Ford pickups. Neither has the ignition resistor. So, I'm looking for 1.5 ohm coils. I ordered one off Ebay from Third Gen Auto. The ad said it was a Petronix, 6 volt, 1.5 ohm coil. Cool, that's what I wanted/needed. So, it shows up and I do some research on-line with the part numbers (B-12000 and # 40011) it turns out it is a 1.5 ohm 12 volt coil. Should I care? Will my 6 volt positive ground system work properly with this 1.5 ohm 12 volt coil? Thanks.
 
You want about 4 amps going through the points; more than that will burn them prematurely and less than that will produce a weak spark. Applying Ohm's Law confirms that on a 6 volt system, a 1.5 amp coil is correct, because 6/1.5=4. 1.5 ohms is 1.5 ohms, so that coil should work. The little I know about Pertronix systems tells me that they don't need a ballast resistor, which checks out. Unless there is some other electronical gimmickry in the Pertronix coil (which I wouldn't know about), it should work OK. I certainly don't think it would harm anything.
 
Copy that...the Ohm's Law math lead me to this coil which was listed as a 6 volt, 1.5 ohm coil in the advertisement on Ebay. With Ohm's Law in mind then I shouldn't care if the coil is labeled as a "12 volt coil" since the coils resistance is 1.5 ohms and that is what my 6 volt positive ground set-ups need? Therefore, a coils resistance is independent of the voltage running through it? Just trying to understand. Electricity is not my strong suit....
 
Years ago, I messed around, running a variety of coils on whatever I had at the time (47 Ford). My bottom line conclusion was/is that a coil is a coil is a coil. I subscribe to what tubman posted regarding the amps. (Idle amps, measured with an old analog gage.) And, in running about a dozen different coils (including a couple from electronic systems), I used resistors as appropriate. I've never run across a situation that has caused me to deviate. Currently, I'm running a 40 Ford that came to me with a 8BA and original 6V coil. The car is on 12 volts. And, I hung a resistor on it, to bring the amps in range. So far, it runs good, starts easy, etc. So, in my opinion, any coil that rings your bell, should work ok. The only thing I might point out.... you say 6V positive ground... So, if you're running a modern 12V coil, be sure to get the polarity correct. For example, on my 40, with 12V system, the old 6V coil looks like it's hooked up backwards, because the old 6V coil is labelled "dist", and "ign", so I had to reverse those two wires. As noted... just opinion....
 
mfirth said:
Two Jail Bar trucks !!!! I'm jealous. Good luck with spark .......
Click to expand...

I've got a few more than two! What was I thinking?!?!
 

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Update: I installed the new Flamethrower 1.5 ohm coil and the truck still would not fire. Yesterday I installed a new Mallory 400 condenser and she fired right up! Success. FYI, the previous condenser was a "new" period correct style condenser that had only been on the truck a year and not used very much at all. As a result I have ordered a number of higher quality condensers (Mallory, Japanese, etc.) condensers to have a stockpile of backups. My guess is my 40 1-ton suffers from the same problem and probably another 47 1/2 ton.
 
For what its worth ..... Optional coil and condensor sourse .... Charlie NY does all my work on ignition and gas system problems and components. He recommmended to me NAPA IC 14 coils ( abt $55 ) and NAPA IH 200 condensors ( abt $22 ). In my case my non-starting problem was my little used Bosch Blue Flame coil.
 
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